House Dust Mites (by Cheryl Mason)

Sneezing, rhinitis, sinusitis, wheezing, asthma, eczema and dermatitis – if you suffer from any of these, read on! These allergies are often related to an organism that lives in our houses, indistinguishable to the human eye – the house dust mite. These tiny organisms are just a third of a millimetre in size – no […]

Sneezing, rhinitis, sinusitis, wheezing, asthma, eczema and dermatitis – if you suffer from any of these, read on!

These allergies are often related to an organism that lives in our houses, indistinguishable to the human eye – the house dust mite.

These tiny organisms are just a third of a millimetre in size – no larger than a tiny speck, and yet the debris from their body and their droppings can cause an allergic reaction in some people who inhale them or come into contact with them.

House dust mites feed on human and animal skin scales as well as bacteria, viruses and moulds. On average, a human sheds 1 gram of skin scales a day – enough to feed many mites for months! House dust is largely comprised of this shed skin, which is why the contents of a vacuum cleaner are usually grey in colour. However skin in its raw state is of little use to the house dust mite. It is too hard, dry and horny; the fat content is too high and the vitamin content too low. Shed human skin needs to be “processed” by certain moulds before it is of interest to a house dust mite.

Nowadays, our warm centrally heated houses are the ideal breeding ground for these creatures, which thrive in damp conditions at a moisture level of 80 per cent relative humidity and a temperature of around 25°C (77°F). The mites live in a harsh environment without liquid and so they have adapted to conserve their internal water very efficiently, burning off carbohydrates to form carbon dioxide and water.

A Year-Round Problem

In the UK, with high humidity conditions, house dust mites thrive all year round, increasing in number during spells of damp weather, at a time when many people notice their allergies are at their worst. This is one reason why asthmatic children often get better on Alpine holidays only to deteriorate on their return. (This is not surprising when we consider that we breathe out 2 pints of water each day).

Beds, duvets, chairs and carpets as well as cushions and curtains are ideal living conditions for house dust mites. They frequently collect in skirting boards where bacteria, food, mould and human skin scales collect. However, these mites are not just confined to the house. They are also found at work in carpets, dusty files and around electrical equipment.

It has been suggested that they can contribute to sick building syndrome, a whole host of symptoms including sore throats, runny noses, headaches etc. Particularly dense concentrations of allergen build up are around VDU screens, because the airborne dust remains suspended and carries an electrical charge which attracts them to electrical equipment.

House dust mites are most likely to cause a problem when they become airborne. Regular vacuuming, changing bed linen, beating rugs and cushions and even moving furniture around will disperse house dust mite allergens into the air. Dr John Maunder reporting in the Independent on Sunday comments “the best thing to do for sufferers is to throw a brick through their bedroom window and forbid them to mend the glass”. As the Director of the Medical Entomology Centre at Cambridge University, he is particularly concerned about the growing number of asthma cases, thought to be due in part to the house dust mite’s dung.

American scientists have shown that the proteins in the faeces are the actual allergens – the substances that cause an allergic reaction.

Dr Feather, a clinical research fellow at Southampton University cites research that shows how remote tribes that live in New Guinea hardly ever suffered from asthma until they were given blankets that were infested with colonies of house dust mites. Building work which involves pulling up skirting boards can cause problems. When heating or fires are switched on, dust mite allergens are drawn into the air by convection currents. If you are unfortunate enough to be living in a damp environment then this will increase the dust mite population. Poor ventilation or even keeping windows tightly shut also contributes to the problem.

Sunlight and a dry environment will kill dust mites as will special aerosol sprays obtained from the chemist. Unfortunately whilst it might kill the mites, their faeces and debris remain.

In most people of course, no harm results from house dust mites and their allergens. But for sensitised individuals it is a different matter as we have seen. The problem often goes unrecognised because the mites are inconspicuous and conditions such as dermatitis can be a result of a reaction to the minute amounts of droppings deposited by the dust mite.

A doctor can test for allergy to house dust mite by means of a simple, non-invasive skin prick test, which is worth considering if you have some of the symptoms outlined above.

Reducing your Exposure to potential allergens

Discard old vacuum cleaners and buy one with a high efficiency filter system.

Improve bed hygiene – a pillow of 6 years can have 1/10 weight consisting of human skin, mites and dung.

Use barrier covers on bedding to provide a protective barrier between house dust mite and the allergic person. (A typical pillow can harbour 2,000 mites, each producing about 20 faecal pellets a day). Keep the house well ventilated.

Avoid drying washing on radiators or using tumble dryers.

Thoroughly clean pet’s living areas daily.

Try using sprays such as Actomite to get rid of mites.

Bath pets weekly and keep them out of bedrooms.

Wash cuddly toys weekly or put them in the freezer for a few hours and limit the number in a child’s bedroom.